Currently 2G (GSM), 2.5G (GPRS) and 3G (UMTS/UTRA) mobile or cellular telecommunications networks (PLMNs) co-exist. A development of the radio access network part of 3G mobile telecommunications is “evolved” UTRA or E-UTRA, also referred to as LTE (Long Term Evolution). “System Architecture Evolution” (SAE) is the development of the core network part of 3G mobile telecommunications. The combined core network and radio network development is sometimes referred to as SAE/LTE. It is desirable for mobile terminals to provide continuous service when moving within an SAE/LTE coverage area and between an SAE/LTE and a UMTS coverage area/2G coverage area.
Mobile telecommunications networks have an active state of communication with their mobile terminals and an inactive/idle state of communication with their terminals. When in the active state, as the mobile terminals move between different cells of the network, the communication session is maintained by performing a “handover” operation between the cells. In the inactive/idle state, as a mobile terminal moves between different cells of the network the mobile terminal performs “cell reselection” to select the most appropriate cell on which to “camp” in order that the mobile terminal can be paged by the network when mobile terminating data is destined for that mobile terminal.
Conventionally, the mobile terminal or network determines whether a handover/cell reselection procedure should be triggered in dependence upon measurements of the radio signals of the cells in the region of the mobile terminal. A filter is applied to the signals (either by the network or by the mobile terminal) which calculates an average (e.g. arithmetical mean) value of these signals over a particular time period. This filtered/average values of the cells are then compared with each other or with a threshold value. In dependence upon these comparisons, cell reselection/handover related procedures are triggered. This cell reselection/handover process generally comprises taking radio signal measurements of neighbouring cells and comparing these to each other and to the radio signal of the current cell to determine which cell provides the best signal strength/quality. Handover/reselection to the best cell can then occur.
Calculations to determine whether to perform a handover from one base station to another base station are performed by the network, whereas calculations whether to perform cell reselection are performed by the mobile terminal.
In the idle/inactive state the mobility state (i.e. fast moving or slow moving) of a mobile terminal can be used to optimise cell reselection parameters. Similarly, in the active state, the calculated mobility state can be used to optimise the handover parameters. In the idle/inactive state the mobility state is determined by the mobile terminal, whereas in the active communication state, the mobility state is calculated by the network. The cell reselection parameters and handover parameters can be set optimally by using a history of mobility state measurements.